Fuse



May 19, 1936. G R BROWN 2,041,590

FUSE

Filed June 9, 1934 Ihvent or: George R. Brown Patented May 19, 1936 UNITED STATES PATENT OFFICE FUSE New York Application June 9, 1934, Serial No. 729,852

2 Claims.

My invention relates to fuses and more particularly to fuses of the totally enclosed, nonrefillable type.

The object of my invention is to provide an improved ,fuse which may be used in a motor circuit and will withstand a high inrush of current during thestarting of the motor and yet will operate satisfactorily on a reasonable overload while the motor is running.

What I consider to be novel and my invention will be better understood by reference to the following specification and appended claims when considered in connection with the accompanying drawing, in which Fig. 1 is a sectional view of my improved fuse; Fig. 2 is a side view partly in section of the fuse link and Fig. 3 is a developed view of the fuse link.

Referring to the drawing, indicates a fuse tube of insulating material which serves as a housing and support for the fuse. Two terminal members i i and I2 are provided which are of the knife blade type and may be connected to the usual spring contact members provided for fuses of this type. Terminal members II and I2 are carried by supports !3 and [4 respectively to which they may be connected by riveting or turning down projections of the terminal member after they have been passed through corresponding holes in the supports. Supports I3 and it are secured to fuse tube I!) by means of screws l5 which pass through openings in the side walls of the fuse tube and into threaded openings of the supports i3 and i4. Connectors l6 and I! are secured to central projections l8 and IQ of the terminal members H and i2 as by soldering or riveting the parts together. Fuse link 20 which is of the cylindrical type is carried by the inner ends of connectors l6 and W. The fuse link 20 is secured to connectors I6 and l! by soldering as shown in the drawing though any means of securing the parts together may be used. As better indicated in Figs. 2 and 3, fuse link 29 has the central section reduced by slots H. the end sections as shown in Fig. 3. When the fuse link is formed into a cylinder the central portion of the fuse link is somewhat compressed until the slots are of substantially the same width throughout their length. This reduces the area occupied by the fuse at its center. The purpose of this reduced section is to fix the point at which the fuse will melt so that it will be substantially the same distance from the ends of the fuse tube l0 and a greater pressure will not be developed at one end of the tube than at the other end.

The central section of slots 2| is wider than Also there will not be any likelihood of an are striking to the support l3 from an adjacent portion of the fuse link and possibly bridging the gap in the fuse link. When an electric current passes through the fuse, the central section of fuse link 20 of reduced area is heated to a higher temperature than other portions of the fuse. When the current exceeds the capacity of the fuse or the section of the fuse link of reduced area, the heat generated is suflicient to melt the fuse link at this point. The melting of the fuse link is not solely dependent upon the density of the current flowing through the fuse but is also dependent upon the time which this excess of current continues to flow. Thus a very heavy overload may be endured for a relatively short time without causing an operation of the fuse. Fuses used in motor circuits are called upon to withstand a high inrush of current on the starting of the motor which may continue for only a short time. However, in some cases the initial. inrush of current may be as much as fifteen times the normal flow of current in the motor circuit while it is running without load. However, it is desirable to insure theoperation of the fuse upon an overload of of the normal load if it continues for many minutes. These conditions are extremely difiicult to satisfy even though the initial inrush of current may not continue for more than a few seconds. To enable the fuse to carry a very heavy overload for a short time and yet operate satisfactorily on a much lower overload for a longer time an increased quantity of metal is provided at each end of the fuse which serves as a heat reservoir to which the heat may be conducted away from the central section of the fuse during the heavy overload. This additional section of metal is provided by turning in from each end of the fuse link 20 integral portions of the fuse links 22 and 23 which are formed on each end of the fuse link 20. The sections 22 and 23 are turned in along the dotted lines of Fig. 2 before the fuse link 20 is formed into a cylinder. The portions 22 and 23 are of sufiicient length so that when turned in the sections 22 and 23 extend to substantially the ends of the slots 2 I. Upon a heavy inrush of current in the motor circuit when it is started the heat which is rapidly generated in the central section of the fuse link 20 is conducted to the ends of the fuse link of much greater section and consequently much greater thermal storage capacity. In actual practice, a fuse constructed to protect a motor circuit and rated 225 amps, 600 volts has operated satisfactorily in the motor circuit in which the normal no load current flow is amps. the initial inrush of current is 930 amps. which continues for 1.38 seconds. The next 1.62 seconds the current drops to 850 amps. and finally dropping in 1.9 seconds to 60 amps. The full load capacity of this fuse is 225 amps. and the fuse will operate at overload in twelve minutes and yet will successfully carry 930 amps. for 1.38 seconds and 850 amps. for an additional 1.62 seconds. A similar fuse without the end sections 22 and 23 to increase the thermal storage of the ends of the fuse link 20 will not carry such a heavy inrush of current. To assist in snufling the are which may be drawn on the melting of fuse link 10, an incombustibie filler 24 is provided and is packed within the fuse tube both inside and outside of the fuse link 20. To retain the filler 24 within the fuse tube I0 end caps 25 and 2B are provided and secured to the tube by means of the screws ii. For additional assurance against loss of the filler 24 and to provide free vent for the gases generated on blowing of the fuse, two cloth discs 21 and 28 separated by an asbestos disc 29 are located at each end of the tube III within the caps 25 and 26.

From the foregoing, it will be seen that an improved fuse is provided which will adequately protect a motor circuit in which the initial inrush of current upon the starting of the motor very greatly exceeds the overload rating of the motor. In addition, a fuse is provided which is eilicient in operation, of low cost of manufacture, and easy to assemble.

What I claim as new and desire to secure by Letters Patent in the United States is:

1. In a fuse, a fuse link of cylindrical shape with longitudinal slots located at the center of the fuse and integral projections from each end which are turned back into intimate contact with the adjacent portions of the fuse to form surfaces of increased heat storage capacity.

2. In a fuse, a cylindrical fuse link with longi-- tudinal slots in the central portion and integral projections from each end which are turned back and extend to substantially the ends of the slots and serve to form surfaces of increased heat storage capacity.

GEORGE R. BROWN. 

